Truck crashes are commonly caused by mechanical failures. Most of these failures are not spontaneous, but progressive, and stem from maintenance deficiencies. Some examples of maintenance deficiencies that cause truck crashes are braking defects caused by oil-contaminated brakes, braking defects caused by brakes that are out of adjustment, tire failures from tires that are run under-inflated or over-loaded, wheel separations caused by wheels and hub assemblies that are improperly installed or maintained, and steering system components that are used and worn to the point where they separate and fail. The standard of care for maintaining and repairing trucks makes the motor carrier and its drivers responsible for keeping their trucks in a safe condition at all times. Since progressive failures can be identified, allegations of mechanical failure are really an admission of motor carrier and/or driver failure rather than an excuse for a truck crash.